Saw



June 2o, 1944. A A N BLUM 2,351,737

SAW

Filed May 9, 1940 2 Sheets-Shed 1 N im June 20, 1944. j A. N. lBLUM 2,351,737

SAW

Filed May 9, 1940 2 Shee'tsQSheet 2 Patented June 20, 1944 UNITED STATES PATENT OFFICE 'SAW Arthur N. Blum, Philadelphia, Pa. Application May 9, 1940, Serial No. 334,242

Claims.

This invention relates to improvements in saws of the type wherein the teeth are all cutting teeth and adapted to cut in both directions of blade movement, as for example in certain socalled pulpwood saws,- and a principal object of the invention is to provide a saw of this type which will combine to a more pronounced degree than heretofore has been found possible the essential functional characteristics of rapidity and accuracy of cut, and easy cutting without chatter.

Another object of the invention is to provide an improved saw, blade of the stated class, which by reason of the form and arrangement of teeth may be readily sharpened and maintained in condition for maximum operating eiciency.

A further object is to provide a blade which will retainits operating efficiency under normal conditions for a longer period of working time than do the prior blades of the same type.

The invention resides in the` novel form, relative arrangement, and set of the teeth of the blade hereinafter specifically described and illustrated in the attached drawings, in which:

Figure 1 is a side View of a section of a saw blade made in accordince with and constituting a preferred embodiment of my invention;

Fig. 2 is an enlarged side view of one of the Y illustrated in Figs. 1 to 6, inclusive, the blade comprises two systems of groups of teeth, the individual groups of each system being similar in the respects `hereinafter noted, but differing from theindividual groupsy of the othersystem.

The said systems are so related that throughout the blade the groups of one of said systems alternate `with the groups of the other of said sysately adjoining.

In the drawings, the individual groups of teeth constituting one of said systems are designated by the reference character A; and B designates edges I.

of the groups A comprises four teeth; each of the groups B two teeth. Each proximate pair of the groups A is separated by one of the lesser groups B; and each adjoining pair of groups, irrespectiveof the systems to which they may belong, is `.separated by a wide major gullet C,'the function of which isto clean the kerf cut by the teeth of the accumulated chips and sawdust. These major gullets define the limits of the aforesaid cutting areas, which areas correspond to the groups A and B.

As shown in the` drawings, `all of the teeth of the blade above their common root line are of the same size and shape. Within the respective groups, the teeth are evenly spaced, and the spacing is the same in both of the groups A andB. Th-e bases of teeth are separated and spaced from each other in the present instance by sharpening gullets D, which are relatively narrower than the major gullets C and have rounded bottoms and are of suicient width to afford ample clearance at the bases of the teeth for correct sharpening, Preferably, and as best shown in 2, both edges of the individual tooth are inclined to the longitudinal axis of the blade and preferably, also, converge from opposite sides of a line which intersects the apex o f the tooth and which is normal to the said longitudinal axis or to the common root line of the teeth, but the inclinations of the edges differ. The broken line rc-gp, which parallels the longitudinal axis of the blade, may be considered the common root line o f the teeth, and y-y the said normal line which inter: sects the apex of the tooth. It will be noted that the edge I of the tooh forms with the line ,q2-g: a relatively steep angle as compared with the angle formed by the opposite working edge. `In ,effect, the root portion of the tooth is multilateral, and this form of root is preferred, although the root may be formed with straight or curved edges without departure from the invention,

In each of the groups A and B the teeth are so` relatively arranged that each of the cleaning gullets C is flanked by two of the relatively steep Thus the teeth of the individual twotooth groups B are arranged relatively so that the edges 2 of lesser inclination are made to face toward the center of the grouprand the opposite edges I, are on the exterior of the group. Similarly the teeth of the individual groups A are arranged relatively so thatthe edge 2 of lesser inclination in each of the teeth faces toward the center of the group. Each of the groups A and B, therefore, is symmetrical with respect to aline the individual groups ofthe other system. Each 55,; `bisecting the group, rand each group A virtually consists of a two-tooth group augmented by twov two teeth which constitute the terminal pair at one end of each of the augmented groups A are, in effect, made to face in the opposite direction from the two teeth at the other end of'th'group".

so that the group is symmetrical with Arespect to a line s-s. In the individual groups "B, the

two teeth face in opposite directions so that each' of these groups also is in thesame, sense. sym metricalj'with'respect to ak medianlirie previously; setjforthgl all offthe'teeth above root* lin-eareidentical'as reforml and size, and

irrespective' ot'grouping, 'the corresponding edges j of' thescorrespondingly placed and set teeth will bparallel l' to` Y'each 1ot h'elr.` A irrespective of set,

the Lnormal projections y upon the" median plane of 'thebladejof .thej corresponding cutting* edges of fall" the teeth,` which edges' iace' in the same direction oi blade motion,A are parallel;l Whilefrin each of the individual cutting areas the arrangement of the teethds symmetrical asset forth above', it visto'jbe noted that the vcutting areas or groups are` -asy-rnmetrically arranged 'with re spect to the maior gullets Cp All teeth are Set aboveftheircomrnon root line i sc fasjt-on avoid deformationof the blade body; proper; ASuchdeformation*or crimping of the blade 4bcdyreduces the effectiveness of thesaw byincreasing friction in 1the kerf and vrequiringmoreforce-'to pullfthe saw-incutting.- l Referring Vto Fig'. 6, it willbe noted that-'wheres as in the'respective' major groupsA the teeth are set alternately to opposite sides of the blade, 'the two teeth ofV each of theininor groups'B are set tohthesame iside. 4Also the proximate; terminal teeth 'f each-proximate pai-noi groupsA areset fr tothe"`same Aside of the blade,k and uthe Vteeth'of Sider Thus menacing tooth for any individual movemen'tfofv the l bladegiwill` enterv l the fkerf 'onf' thelovppo'site-'s'ide of theblade from? the leading teethof theV proximatecorresponding groupsj The` sam'efv result may be obtained 'b-ysetting the teeth in the manner illustrated 'in Fig; 7, whereinA the two'teethor"t'ern1inalfpair of teeth at oneendlof'each of the* groups-1A are/set to "the" same sideof the'blad'e and 4(the remaining Ytwo` teeth to the oppositeside. By settin'g'the teeth in pairs in this manneradded lresistance to loss of set is obtained, in that" the set of eachA tooth is immediately reinforced by the set of a corn-r panion tooth.

In conventional bladeshaving 'tee'thf grouped incutting areas of equal-width and of lan equalY f number of teeth,'even1y`,or substantially evenly spaced, there is atendency yfor tlieiblade'to chat-l ter. `I The blade' is highly tensioned in the frame,

and-when avtooth strikesan obstruction; it starts' a train-of vibrations which 'are syn'chron'ouslyin'- tensified'l the subsequent teeth? if they' are l grouped in' areas of equal length and "substantiall'yl 1 evenly-'fspacedj v-In a blade made in* accordance uneven lengths, one of Which is short and contains only two teeth, such intensification of the' vibrations of the blade is dampened out, substan-` ti ally reducing or eliminating the chatter. It has been proposed to accomplish similar results by uneven spacing of theteeth alone in blades with conventional cutting areas having equal number' of teeth, but to be effective, the diierence inY spacing of the latter would have to be Very pro' nounced and of an orderj entailing a decidedfvariability of the tooth pitch, which is not desira' ble for practical reasons. i

The setting of the teeth described above, Which provides that the leading tooth in each groupY in*- Hboth directions of blade movement will enter the kerf at "the opposite side of the blade from! either of the leading teeth of the proximate like groupst effects 'a 'substantial balance in the operation of the-,blade which insures a. proper tracking of thel blade in the intended plane of cut, andlargely precludes 4the'y tendency exhibited' 'by fther `forms: or biadeofthis genere-'1 type jto cut'ma'ceurateiy or off; the normal plane. Also 'as' previously set', forth,'jthe setting otwol adjoining teeth to same' side of the. bladefmate'rially increases the resistance f the teeth toflossiof'set, so :that vthe blade will maintain itsoper'ating eiciency for` longer lperiods of time thar'where'theteeth are set in the normal"manner'alternatelyvv to opposite lsides 'of' the 'blade This "setting of two teeth together not only has the favorableeect noted above upon the twoV teethuimmediately involved, but also helps to rmaintain the set ofV the other teeth of theblade. AvAsindicate'd above, the'fact" that the It'eetlfi are uniform'a's to size 'and Shape and are 'uniformly' and adequately spaced mate'- ria'll'y vsimplifies'. the sharpening and resharpen.- ing operations' and maintenance of the Jblade in its 'original-state of high" functional efficiency. When'th'e teeth 'of a blade constituted as de scribed above' are'eiliciently sharpened,` for example'inthe y'manner novvvv to be'des'cribed, the, blade willexhibit'in prc" 'no1incedV degree the coQmf'ff bined characteristicsof Veasyl cutting Without. chatter and rapidity and accuracy of cut. Asi; previously'stated, both edges of the individual'` tooth constitute'active cutting edges. `Both of` the edges .l and'2 are beveled' at the same side of the tooth, the beveled surface being indicatedV by the reference'num'eralsft kand YIl respectively, These surfaces are inclined' to 'the' lines' 5 and which represent; respectively, the corners of the inclined edges l and 2 at the unbeveled side Of the toothf and as'aresult; a portion oieachof the edge surfacesml 'and '2 ,is left unaffected, Theseunaifected areas; whichoccupyplane's 'sub stantially normali to "the plane sides 'of the'blade," are designated by the reference numerals Vl andi" 8. The bevels S'and 4 are formed so as to inter- :sectv the Aplane'of theopposlte side'of'the tooth', l

only'v within a limited area immediately ad'join'-v ingthetipg's'o that at the'tip the tooth' is slightly truncated; This'is clearly shownin Fig.' 2. The

eiect'is to' form at eachside of ythe tip a clearly "deiined sharp cutting'edga 9 and'l respectively;H

of substantiali'length; which produce 'a slicing drawing ycut in both directions of'blade"movemel;i t;

these' edges 'constitutingv the lines of intersection of thelbevels :i and '4u/'ith the planev ofthe'un beveled'side of thetooth, and the convergence of these lines or cutting edges forms theap'ex' of the tooth.' In generalgtheactual lengths 'of thecut= ting'edges'g and fit) should notcvery materially" exceedthe" actual 'thicknessV of the unsharpened,

blade' 'at the"breast`,` 'i. e.: the" thickness'of the.

tooth at the tipprior to sharpening. More speciflcally, it is preferable that the said cutting edges do not exceed in length approximately 150% of the said unsharpened breast thickness.

The manner in which the tooth is set is illustrated in Figs. 3, 4 and 5. As therein shown, the

ing the latter on a line extending approximately through the centers of the arcs at the bottoms of the spacing gullets D, which, as shown in Fig. 2, is above the common root line :1x-:r and leaves the blade proper unaffected by the bending of the teeth the offset portions of the teeth retaining their flat form, as previously set forth. 'Ihis ilat or straight set increases the effectiveness of the cutting edges 9 and I9 and operates to limit the extent to which the tip of the tooth digs into the work. The kerf produced by a saw having this character of tooth and set is relatively smooth and uniform.

In conjunction with the shape of the cutting edges above described, the straight set and its amount have an effect upon the cutting action of the blade and the ease with which it is performed. I have found that for best results, the total set of the blade, equalling the sum of the sets of two teeth set to the right and left respectively, should be less than 200% of the thickness of the unsharpened blade at its breast. This amount of set must be maintained for continuous best performance of the saw, which is difficult, in case of the so-called pulpwood saws, made of thin steel,

because the side pressure in the kerf while cutting has a tendency to bend the teeth back into the plane of the blade and in time to reduce the initial set. As previously described, this tendency may be counteracted by setting two teeth in succession to one side of the blade so that the set of one tooth reinforces the set of the subsequent one, and this also, by maintaining the width of the kerf, relieves the pressure on others of the teeth. By limiting the total set of the blade as described above, the bevel edges Il (see Fig. 4),

of two succeeding teeth set to opposite sides of the blade (which edges H deiine the conjunction of the bevel faces 3 and 4), will, in projection, intersect within their respective lengths. In this manner, the work will be scored and cut by the cutting edges 9 and I0 on both sides of the kerf, and the slug thus prepared will be removed by the raking action of the portions of the teeth adjoining the said cutting edges, the kerf being swept by the in-projection-overlapping faces of the teeth near the tip. In other words,\the said edge II of each of the teeth of the blade will be intersected by a median plane, indicated in Fig. 4 by the broken line z-e, bisecting the thickness of the blade. It will be understood, of course, that the inclination of the edges Il to the plane of the tooth, which inclination is determined by the angle of the faces 3 and 4 to the same plane, should be such as to afford the beveled tip ofthe tooth an adequate major thickness and strength, and when this is observed, the said median plane will intersect the edges Il relatively close to the apices of the teeth and within the area of the how the three variables, namely, thegrouping of the teeth in unequal cutting areas, their setting and their sharpening, are tied together functionally to produce the highly advantageous results claimed for my invention.

The various structural features described above contribute jointly to the production of a blade which exhibits extraordinarily easy cutting without chatter, and extreme rapidity and accuracy of' cut, and one which not only maintains these characteristics for relatively long periods of use but which may be readily resharpened and maintained in its original high operating efiiciency. It is to be noted, however, that while the various structural features will augment each other to an extent aording exceptionally good results in combination, certain of these features individually are capable of effecting a material improvement in the functional characteristics of any saw in which they may be incorporated. It is apparent, therefore, that there may be a substantial modification of the blades herein specifically described. Two such modifications are illustrated in Figs. 8 and 9 of the drawings. In each of these modifications, the form and group arrangement of the teeth are the same as previously described, but the two teeth in each of the groups B are set respectively to opposite faces of the blade. It will be apparent that certain of the benefits of the invention as defined in the appended claims will accure to these modifications.

I claim:

1. A saw blade having exclusively cutting teeth of substantially uniform height and size each set to one or other side of the blade, said teeth being separated yby gullets including large cleaning gullets and smaller sharpening gullets, said sharpening gullets having their bottoms aligned cn a common root line and said cleaning gullets having their respective bottoms also aligned on a line parallel to said root line, each of said teeth having oppositely beveled and sharpened knifelike cutting edges converging and terminating ln a scalene cutting point adapted to slice in both directions with a drawing cut, said cutting edges being inclined to said root line but at different angles other than and the normal projections upon the median plane of the blade body of the corresponding cutting edges of all the teeth, which edges face in the same direction of blade movement, :being parallel, said teeth being arranged in symmetrical two-tooth groups having their beveled and sharpened cutting edges of steeper inclinations situated on the exterior of said two-tooth groups, each alternate two-tooth group :being augmented by anking teeth having their cutting edges facing in the same direction of blade movement as the corresponding edges of the respective immediately adjoining teeth of the associated two-tooth group, the augmented groups being separated from the intervening unaugmented two-tooth groups by said large cleaning gullets, and the two teeth flanking each of the large gullets being set respectively and entirely above their respective roots to the opposite sides of the blade, the set of each side of the blade not exceeding in amount the unsharpened breast thickness of the blade.

2.- A saw blade having exclusively cutting teeth of substantially uniform heightand size, each set to one or other side of the blade, said teeth being separated by gullets including large cleaning gullets and smaller sharpening gullets, said sharpening gullets having their bottoms aligned on a common root line and said cleaning gullets `having their respective bottoms also aligned on a parallel to said root line, each of said lteeth having oppositely beveled and sharpened knifelike cutting edges converging and terminating in a scalene cutting point adapted to slice in both directions with a drawing out, said cutting edges 'being inclined tosaid root line `but .at different angles other than 90, and the normal projections Yupon the median plane of the blade body of the corresponding cutting edges of all the teeth,

lwhich edges face in the same rdirection of blade movement, being parallel, said teeth being arranged in symmetrical two-tooth groups with each alternate group augmented by two additional teeth one at each end of the group, the

teeth of the two-tooth groups having their beveled and sharpened cutting edges ofsteeper inclinationisituated on the exterior of said twotooth groups and each of said augmenting teeth having its cutting edges facing in the same direction of blade movement as the corresponding ledges of the adjoining teeth of the augmented 3. A saw blade having exclusively cutting teeth` of substantially uniform height and size, each set to one or other side of the blade, said teeth being separated by gullets including large kcleaning gullets and smaller sharpening gullets, sharpening gullets having their bottoms aligned on a common root line and said cleaning gullets 4having their respective bottoms also aligned on a parallel to said root line, each of said teeth having oppositely beveled and sharpened knifelike cutting edges converging and terminating '1n a scalene cutting point adapted to slice in both directions with a drawing cut, said cutting edges being inclined to said root line but at different angles other than 9D", and the normal projections upon the median plane of the blade body of the corresponding cutting edges of all the teeth, which edges face in the same direction of blade movement, being parallel, said teeth being arranged in symmetrical two-tooth groups with each alternate group augmented `by two additional teeth one at each end of the group, the teeth of the two-tooth groups having their beveled and sharpened cutting edges of steeper inclination situated on the exterior of said twotooth groups and each of said augmenting teeth having its cutting edges facing in the same direction of blade movement as the ,corresponding edges of the adjoining teeth oi the augmented two-tooth group, and the augmented groups being separated from the intervening unaugmented two-tooth groups bysaid large cleaning gullets, the teeth oi each terminal pair in the augmented groups being set together to one side oi the blade with the said pairs in any one group set to opposite and the teeth of each of the two-tooth groups being similarly set together to one side of the blade and to the opposite side from the proximate terminal' pairs of teeth in the .immediately adjoining augmented groups.y

4. A saw blade having exclusively cutting teeth of substantially uniform heightiand size, each set to one or other side of the blade. vsaid .teeth being separated by gullets including large cleansaid ing gullets and smal'ier sharpening yguliets, said 75 sharpening gullets having ltheir bottoms aligned on a vcommon root line and said cleaning gullets having their respective bottoms also aligned on a parallel to said root line, each of `said teeth having oppositely beveled and sharpened knifelike cutting edges converging and terminating in `a scalene cutting point adapted to slice in both directions with a drawing cut, said cutting edges Ibeing inclined to said root line but at diierent angles other .than and the normal projections upon the median plane of the blade body of vthe .corresponding cutting edges of all the lteeth, which edges face in the same direction of .blade movement, being parallel, said teeth being arranged in symmetrical two-tooth groups with each alternate group augmented by two additional teeth one at each end of the group, the teeth of the two-tooth groups having their beveled and sharpened cutting edges of steeper 'inlclination situated on the exterior of said twotooth groups and each of said augmenting teeth having its cutting edges facing in the same direction oi blade movement as the corresponding edges of the adjoining teeth of the augmented two-tooth group, and the augmented groups being separated from the intervening unaugmented two-tooth groups by said large cleaning gullets, the two teeth of the two-tooth groups being -set together to one side of the blade, and the teeth in each of the augmented groups being set alternately to the opposite sides of the blade,

.5. A saw blade having exclusively cutting teeth of substantially uniform height and size, each set to one or other side of the blade, said teeth -being separated by gullets including large cleaning gullets and smaller sharpening gullets, said sharpening gullets having their bottoms aligned on a common root line and said cleaning gullets having their respective bottoms also aligned on a parallel to said root line, each of said teeth having oppositely beveled and sharpened knifelike cutting edges converging and terminating in a scalene cutting point adapted to slice in both directions with a drawing cut, said cutting edges being inclined to said'root line but at diffe-rent angles other than 90, and the normal projections upon the median plane of the blade body of the corresponding cutting edges of all the teeth, which edges face in the same direction `of blade movement, being parallel, said teeth being arranged in symmetrical two-tooth groups with eachalternate group augmented by two additional -teeth one at each end of the group, the teeth of the two-tooth'groups having their beveled andsharpened cutting edges -of steeper inclination situated on the exterior of said -twotoothfgroups and each of said augmenting teeth Vhaving its cutting edges facing in the same direction of blade movementas the corresponding edges of the adjoining teeth of the augmented two-tooth group, and the augmentedgroups being separated from the intervening unaugmented two-tooth groups by said large cleaning gullets, the teeth being set so that for both directions .of'blade movement the leading teeth of any one of the groups containing the larger number of teeth is set to the opposite side of the blade from the leading tooth of the next following group containing the larger number of teeth, and to 4the same side of the blade as the leading tooth of the intervening two-tooth group.

6. A saw blade having exclusively cutting teeth of substantially uniform height and size each set vto .one or other side ofthe blade, saidteethrbeing :separated by gullets including large cleaning gullets and smaller sharpening gullets, said sharpening gullets having their bottoms aligned on a common root line and said cleaning gullets having their respective bottoms also aligned on a line parallel to said root line, each of said teeth having oppositely beveled and sharpened knifelike cutting edges converging and terminating vin a scalene cutting point adapted to slice in both directions with a drawing cut, said cutting edges being inclined to said root line but at diiferent angles other than 90, and the normal projections upon the median plane of the blade body of the corresponding cutting edges of all the teeth, which edges face in the same direction of blade movement, being parallel, said teeth being arranged in symmetrical two-tooth groups hav- ,ing their beveled and sharpened cutting edges of steeper inclinations situated on the exterior of said two-tooth groups, each alternate two-tooth group being augmented by flanking teeth having their cutting edges facing in the same direction of blade movement as the corresponding edges of the respective immediately adjoining teeth of the associated two-tooth group, the augmented groups being separated from the intervening unaugmented two-tooth groups by said large cleaning gullets, the teeth being set so that for both directions of blade movement the leading tooth 'of any group is set to the same side as the leading tooth of the next following group having the same number of teeth.

7. A saw blade having teeth of substantially the same size and shape, each sharpened and set so as to cut in both directions of blade movement,

the cutting edge of the blade consisting of alternately arranged groups of two and four teeth respectively and intervening chip removing gullets, the bases of the teeth of each group being separate and spaced apart, one edge of each tooth being relatively steep as compared with the other edge with respect to the longitudinal axis of the blade and the teeth beine,r arranged in the respective groups so that the edges of lesser steepness face toward the centers of the groups, the individual teeth having both edges beveled at the same side of the tooth with each of the bevels intersecting the other side of the tooth only Within a limited area immediately adjoining the tip and forming at said intersection a sharp cutting edge terminating in the apex of the tooth, and each said individu-a1 tooth being set to the side of the blade away from the bevel face of the tooth and to an extent such that the total set of the blade shall be not more than approximately 200% of the thickness of the unsharpened blade at the breast.

8. A saw blade having teeth of substantially the same size and shape each sharpened and set so as to cut in both directions oi blade movement, the cutting edge of the blade consisting of alternately arranged groups of two and four teeth respectively and intervening chip-removing gullets, the bases of the teeth of each group being separate and spaced apart, one edge of each tooth being relatively steep as compared with the other edge with respect to a longitudinal axis of the blade and the teeth being arranged in the respective groups so that the edges of lesser steepness face toward the centers of the groups, the individual teeth having both edges beveled at the same side of the tooth with each of the bevels intersecting the other side of the tooth only within a limited area immediately adjoining the tip and forming at said intersection a sharp cut ting edge terminating in the apex of the tooth and not exceeding in length approximately 150% of the thickness of the unsharpened blade at the breast, each said individual tooth being set to the side of the blade away from the bevel faces of the tooth and to an extent such that the total set of the blade shall be not more than approximately 200% of the said unsharpened breast thickness of the blade.

9. A saW blade having teeth of substantially the same size and shape, each sharpened and set so as to cut in both directions of blade movement, the cutting edge of the blade consisting of a1- ternately arranged groups of two and four teeth respectively and intervening chip removing gullets, the bases of the teeth of each group being separate and spaced apart, one edge of each tooth being relatively steep as compared with the other edge with respect to the longitudinal axis of the blade and the teeth .being arranged in the respective groups so that the edges of lesser steepness face toward the centers of the groups, the individual teeth having both edges beveled at the same side of the tooth with each of the bevels intersecting the other side of the tooth only within la limited area immediately adjoining the tip and forming at said intersection a sharp cutting edge terminating in the apex of the tooth, each said individual tooth being set te the side of the blade away from the bevel face of the tooth and to an extent such that the total set of the blade shall be not more than approximately 200% of the thickness of the -unsharpened blade at the breast, and the common line of intersection of said bevel faces in each said individual tooth being intersected by a median plane bisecting the thickness of the blade.

10. A saw blade having teeth of substantially the saine size and shape each sharpened and set so as to cut in both directions of blade movement, the cutting edge of the blade consisting of alternately arranged groups of two and four teeth respectively and intervening chip-removing gullets, the bases of the teeth of each group being separate and spaced apart, one edge of each tooth being relatively steep as compared with the other edge with respect to a longitudinal axis of the blade and the teeth being arranged in the respective groups so that the edges of lesser steepness face toward the centers of the groups, the individual teeth having both edges beveled at the same side of the tooth with each of the bevels intersecting the other side of the tooth only within a limited area immediately adjoining the tip and forming at said intersection a sharp cutting edge terminating in the apex of the tooth and not exceeding in length approximately 150% of the thickness of the unsharpened blade at the breast, each said individual tooth being set to the side of the blade away from the bevel faces of the tooth and to an extent s-uch that the total i set of the blade shall be not more than approximately 200% of the said unsharpened breast thickness of theV blade, and the common line of intersection of said bevel faces in each said individual tooth being intersected by a medi-an plane bisecting the thickness of the blade and at a point Within the area of said cutting edges.

ARTHUR N. BLUM. 

